Table 2.

Quality indicators from Newcastle-Ottawa scale

Study	Selection				Comparability		Exposure/Outcome			Score
	1	2	3	4	5a	5b	6	7	8
Hemminki 2010	yes	yes	yes	yes	yes	Yes	Yes	Yes	yes	9
Stattin 2007	yes	yes	yes	yes	yes	yes	no	yes	yes	8
Atchison 2011	yes	yes	yes	yes	yes	yes	yes	yes	yes	9
Wotton 2011(a)	yes	yes	yes	yes	yes	no	yes	yes	no	7
Wotton 2011(b)	yes	yes	yes	yes	yes	no	yes	yes	yes	8
Yood 2009	yes	yes	yes	yes	yes	no	yes	no	yes	7
Wideroff 1997	yes	no	yes	yes	no	no	yes	yes	no	5
Adami 1991	yes	no	yes	yes	no	no	yes	yes	yes	6
Ragozzino 1980	yes	no	yes	yes	no	no	yes	yes	yes	6

Footnote: 1, indicates exposed cohort truly representative; 2, the non exposed cohort drawn from the same community; 3, ascertainment of exposure by secure record or structured interview; 4, outcome of interest was not present at start of study; 5A, cohorts comparable on basis of sex and age; 5B, cohorts comparable on other factor(s); 6, quality of outcome assessment; 7, follow-up long enough for outcomes to occur; and 8, complete follow up